Roaming the flood champaign of westerly North America during the Late Jurassic Period , the pith - eatingAllosaurus jimmadseniwas or so 1,800 kilograms ( 4,000 pounds ) and 8 to 9 meters ( 26 - 29 foot ) long . In its ecosystem it was the most usual and the top predator , due to its comparatively tenacious legs and tail , and long limb with three shrewd chela .
The “ Allosaurus ” part of the name translates as “ dissimilar reptilian ” whilst the latter part honor the recent Utah State Paleontologist James Madsen Jr. who excavated and studied tens of thousands ofAllosaurusbones .
Although this paper only recognizes two species ofAllosaurus(fragilisandjimmadseni ) recover in North America , paleontologist argue that there could be up to 12 . Setting this coinage aside from other members of the two - legged carnivorousAllosaurusgenus , who endure during the Jurassic and Cretaceous period , swear on an examination of its head .
“ The skull ofAllosaurus jimmadseniis more lightly built than its later relativeAllosaurus fragilis , suggesting a unlike feeding demeanor between the two,”explainedco - lead generator Mark Loewen , research companion at the Natural History Museum of Utah . Other unequaled feature of the new species include a facial summit stretching down its unforesightful narrow skull from the horns in front of the eyes to the nozzle , as well as a two-dimensional surface under the eyes .
The first specimen ofAllosaurus jimmadseniwas learn at one of the most fertile reference of dinosaur fossils in North America , theMorrison FormationofDinosaur National Monument . On July 15 , 1990 , George Engelmann of the University of Nebraska was bear out a contracted paleontological stock at the site when he come across the headless frame . During the excavation of the site which followed , explosives had to be used to come away the 2,700 - kilogram ( 5,952 pounds ) skeleton block from the surrounding rock before a whirlybird was used to fly it out .
The absent head teacher of the dinosaur was reunify with its body six year subsequently after Ramal Jones of the University of Utah used a Geiger counter to settle the radioactive skull . This written report provides a complete description of every bone of theAllosaurus jimmadseniskull uncovered and a comparison to the skull of other carnivorous dinosaur .
Another “ spectacularly complete ” skeletal frame of the Allosaurus jimmadseni call “ Big Al ” ( MOR 693 ) was expose in Wyoming in 1991 . Scott Hartman
" Recognizing a young species of dinosaur in rocks that have been intensely investigated for over 150 years is an undischarged experience of discovery , ” said Daniel Chure , retired palaeontologist at Dinosaur National Monument and co - lead author of the study . “ Many more exciting fossils wait discovery in the Jurassic rocks of the American West . "
